Midway through the 26-race regular season there has been a tectonic shift of power in the Sprint Cup series. Joe Gibbs Racing has emerged as the sport's top team, overtaking Hendrick Motorsports, which has won the last four championships with driver Jimmie Johnson. Ever since the spoiler replaced the rear wing on the Cup cars at Martinsville on March 29, the JGR duo of Kyle Busch and Denny Hamlin has been the class of the field, winning five of the last eight races. Can the two keep it up? It's one of five questions to ponder in the second half of the regular season.

1.Will anyone catch Gibbs?

No team did more work in the wind tunnel than Gibbs to prepare for the spoiler, which has changed the handling of the cars. But technology gains and setup secrets usually "bleed out in the garage," as one crew chief puts it, so the mechanical advantage currently enjoyed by Busch and Hamlin likely won't last the entire season. And it's entirely possible that Busch and Hamlin could sabotage themselves; after the two collided during the All-Star race in Charlotte on May 23, Busch said over the radio that he wanted to "kill" Hamlin. At the behest of Joe Gibbs, the two have since made nice, but this is a tenuous truce.

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The leader in the standings, Harvick has consistently finished races in the top 10 but has only one victory. His season is looking a lot like Tony Stewart's '09 campaign, in which Stewart won the regular-season points title but faded in the Chase and wound up sixth in the final standings. Harvick, who signed a multiyear contract extension with Richard Childress Racing last week, needs to show more straight-line speed to be a factor this fall.

3.What's wrong with the champ?

Johnson has already committed more on-track blunders this season than he has in the past four combined. He has caused accidents, been busted for speeding on pit road at key moments, feuded with teammate Jeff Gordon and, most significant, struggled to adapt to the spoiler. Should Johnson, currently seventh in the standings, be worried? Not yet, because the number 48 team traditionally starts fast (which they did this year, winning three of the first five races), slows down in late spring, then peaks as the Chase nears. The question is whether the relentlessly efficient 48 team can find a way to come to grips with the spoiler and help get Johnson back into that championship groove.

4.Can Roush-Fenway Racing win a race?

Since RFR's last win, in March 2009, the team's four drivers—Greg Biffle, Carl Edwards, Matt Kenseth and David Ragan—have gone a total of 188 starts without taking a checkered flag. But this team is a sleeping giant; Roush has as many resources as Gibbs and Hendrick, and the consensus in the garage is that the team is on the cusp of a breakthrough. "It's just getting the setup right," Edwards explains. "If we can get that better, then we'll lead laps and win races."

5.Will Dale Earnhart Jr. rebound?

NASCAR's most popular driver is in danger of missing the Chase for the second year in a row. Now 17th in points, Earnhardt faces a critical month. The next four tracks on the schedule—Pocono (career average finish: 17.4), Michigan (15.9), Sonoma (21.4) and New Hampshire (17.8)—are among his worst. If Junior can't find a way to communicate better with crew chief Lance McGrew, his Chase hopes could be stalled by July.

Team owner Chip Ganassi came within .737 seconds of a perfect Memorial Day weekend of racing. Two hours after he won the Indianapolis 500 with driver Dario Franchitti on Sunday (page 50), Ganassi hopped on his private jet and flew from Indy to Charlotte Motor Speedway for the Coca-Cola 600. There, he watched his driver Jamie McMurray(below) finish second—by that .737-second margin—behind Kurt Busch. Though McMurray hasn't won since the season opener at Daytona, he's been one of the top drivers in the Cup series over the last month. In his last five starts, he has three second-place finishes. Currently 15th in points, McMurray looks like a good bet to crack the top 12 by September and qualify for his first Chase.

TWO PHOTOSNIGEL KINRADE/AUTOSTOCK

HOT COMBO Since the debut of the spoiler, Busch (18 and left)and Hamlin have taken five of eight checkered flags.